Angular 4 等待 promise/observable 进入循环

Question

I can't find a valid solution for following case

I want to create the following loop :

1. ForEach elemenent (A) of an array
2. Populate a new array (B)
3. If key doesn't exists in array (B) call a firebase service getting data
4. Verify data and update Statistic
5. at the end of all (A) key, generate statistic of execution and expose...

I need to wait and chain the response of Firebase data before continue the loop, and the problem is that I need to interact with data from firebase in the main loop ( so I can't implement it in subscribe or then )

This is the Part of code that i want to create :

        // Here i check if user exist in array (B)
        let IDUtente = RifEvento.esisteUtente(Ordini.IDUtente) ;

        // If not exists i'll get data from FIREBASE
        if (IDUtente == -1) {
           let NewUser = new TipoStatUtente() ;
           NewUser.Chiave = Ordini.IDUtente ;
           IDUtente = RifEvento.Utenti.push(NewUser) ;
           IDUtente = IDUtente - 1 ;

           // I NEED to wait the end of this function before continue with loop
           this.statoUtente.getUser(IDUtente).then(dati => {
              console.log('Sottoscritto dati utente') ;
              let user : TipoSingoloUtente = dati ;
              NewUser.sonoscuola = user.sonoscuola ;
              if (!NewUser.sonoscuola) NewUser.Intestazione = user.Cognome + ' ' + user.Nome ; else NewUser.Intestazione = user.Scuola.Nome ;
              if (NewUser.sonoscuola) RifEvento.NumScuole += 1 ; else RifEvento.NumUtenti += 1 ;
           })

        }

        console.log(IDUtente) ;

        // Utente Esiste aggiorno le sue statistiche
        RifEvento.Utenti[IDUtente].Commissioni  += Ordini.costoCommissione ;
        RifEvento.Utenti[IDUtente].Incasso      += Ordini.parziale ;
        if (Ordini.Tipo == 'T') {                  
           RifEvento.Utenti[IDUtente].NumTicket += Ordini.numbiglietti ;
         } else {
           RifEvento.Utenti[IDUtente].NumIscritti  += 1 ;
           RifEvento.Utenti[IDUtente].NumBallerini += Ordini.IDBallerini.length ;
          }



      }

And this is the function :

getUser(IDUtente) : Promise<TipoSingoloUtente> {
return this.db.object('user/' + IDUtente).map(users => {
return users ;})
.first()
.toPromise(); }

Answer 1

Maybe this pseudocode can show the implementation for put the asynchronous call in the loop and make sure all the calls are finished then do something .

global count = 0
loop A[i] i:0->A.size
    var B
    if(A[i] NOT IN B)
        async_function(A[i], callback(result))
    else
        //do something
        count++ 
    end if  
end loop A

callback(result)
    //do something
    count++
    if count == A.size 
        //all data has been processed
        //you also can only count the asyn calls
        //final report
    else
        //do nothing
end callback